The present invention generally relates to devices for relief grinding blades, particularly to devices for relief grinding blades of mower reels, and specifically to mower reel blade relief grinding devices utilized in a table-type sharpening system including a spin grinding device.
When manufactured, mower reels are ground to be perfect cylinders. The diameter at all points is equal. The bed knife is mounted so it is perfectly parallel to the blade surface across the full width of the mower. When the blades and knife are properly aligned the best cut is obtained.
Usually two things happen to cause a reel to lose its shape and become tapered. First, most cutting units require that field adjustments be made to keep reel and bedknife in the best cutting proximity. Excessive adjustment on one side causes the reel blades on that side to wear faster. Repetition of the overadjustment actually compounds the problem. The reel loses its cylindrical shape and becomes tapered. The second reason reels lose their cylindrical shape is traced to the very nature of the reels themselves. The natural helix (or twist) in the reel blades causes the "lead in" end of the reel to wear faster. The diameter at that end becomes smaller. Each time the mower reel is adjusted, the accelerated wear continues and the "lead in" diameter becomes even smaller.
If the simple "touch method" of alignment for sharpening is utilized where each end of the mower reel is contacted with the grinding wheel, the reel's conical or tapered condition is not corrected and the reel is not restored to a true cylinder. The difference between the two ends continues to increase, and eventually the taper exceeds the mower's range of adjustment.
To remove the conical shape and restore the reel back to a sharp cylindrical shape with all blade cutting edges ground to the same distance from the reel shaft, a grinding wheel is rotated and moved along an axis parallel to and spaced from the reel shaft while the reel is rotating on the reel shaft. One type of system utilized to spin grind a mower reel and which has been very commercially successful is of the table top variety. Specifically, the reel is mounted by suitable means above a table and with the reel shaft being parallel to and spaced from a grinding shaft. The grinding wheel is rotatable with but axially movable along the grinding shaft.
However, although table top grinding systems have been very successful in spin grinding, prior to the present invention they were unable to provide relief grinding of the blades of the mower reel. Relief grinding removes the excess steel behind the cutting edge (particularly on thick or heavy bladed reels) to allow the reel to operate with less wear and tear on its cutting surface and mow with less power consumption by the mower.
Thus, a need has arisen for a device for providing relief grinding of blades of a mower reel which can be utilized with a rotating grinding shaft and particularly which can be utilized in a table top grinding system.